I’ve received the latest list from TfL via a Freedom of Information request. It confirms my suspiscion that the helpdesk didn’t know what they were saying when they told me that the Finsbury Park OSI was 90 minutes. As I thought, it is actually 10 minutes, which is quite reasonable for the short distance involved. There are also two new interchanges which will happen on May 22nd: Bank to Cannon Street NR (about time I hear you all say) and Putney to East Putney. Full details are on the OSI page of this site. There is also a description of Emergency OSIs which are applied as and when required, usually for short-term engineering work or station closures. Unusually, this mechanism is being used in a semi-permanent way to provide alternative interchanges for Tottenham Court Road while the Northern line platforms are closed.